Vehicle restraints are employed to prevent accidental movement of a truck away from a loading dock during a loading operation. When the truck is parked in front of the loading dock, the rear end of the truck completely encloses the doorway in the loading dock with the result that the truck driver cannot observe the loading or unloading of cargo from the truck by a lift truck or other mechanical handling equipment. To prevent the truck from accidentally pulling away from the dock before the loading or unloading operation is completed, vehicle restraints have been used which are mounted on the loading dock and engage the ICC bar located at the rear end of the truck. The ICC bar is a bar or beam that extends horizontally across the rear of the truck beneath the truck bed and is intended to prevent an automobile from underriding the truck in the event of a rear end collision.
Certain types of vehicle restraints employ a pivoting hook that is pivoted from a lower storage position to an operative position where it engages the ICC bar while other vehicle restraints, such as that disclosed in U.S. Pat. No. 4,488,325, employ a linear moving hook which is moved vertically along the front face of the dock from a lower storage position to an upper operative position where it engages the ICC bar.
During a loading operation the truck bed may rise and fall relative to the dock as a forklift truck moves between the dock and the truck bed. In addition, the truck bed will also rise relative to the dock as cargo is unloaded from the truck bed, and conversely, the truck bed will fall relative to the dock as cargo is loaded onto the truck bed and the truck springs are compressed. It is important that a vehicle restraint have the capability of maintaining the hook in engagement with the ICC bar as the truck bed floats relative to the dock. In certain instances, depending upon the truck, the float can be up to ten inches.